Powdered polysaccharide-reinforced elastomer masterbatches, compounds, and resulting vulcanized rubbers

ABSTRACT

Powdered elastomer masterbatches are prepared by grinding dried rubber curds which contain highly effective reinforcing agents. Such finely comminuted elastomer masterbatches provide stable powdered rubber compounds when blended with usual powdered curatives and fine particle fillers. These powdered rubber compounds are formed into finished vulcanized rubber articles by direct heat-compression molding, by extrusion from a simple machine, or by injection molding without prior high shear mixing.

United States Patent Buchanan et al.

[ 1 June 27, 1972 [541 POWDERED POLYSACCHARIDE- REINFORCED ELASTOMER MASTERBATCHES, COMPOUNDS, AND RESULTING VULCANIZED RUBBERS Inventors: Russell A. Buchanan; Charles R. Russell,

both of Peoria, 111.

The United States of America as represented by the Secretary of Agriculture Filed: July 24, 1970 Appl. No.: 58,187

I73] Assigncc:

US. Cl. ..260/17.4 BB, 260/17.2, 260/17.4 ST,

260/17.5, 260/749 Int. Cl ..C08c 9/12, C08d 9/06, C08f 45/14 Field of Search ..260/17.4 BB, 17.4 ST

[56] References Cited UNITED STATES PATENTS 3,015,640 1/1962 Weaveretal ..260/26 Furtterer ..152/211 Beber et a1 Buchanan et 111..

Douglas et al. Morris et a1. ..260/41.5

Primary Examiner-William H. Short Assistant Examiner-Edward Woodberry A!t0mey-R. Hoffman and W. Bier ABSTRACT prior high shear mixing.

9 Claims, No Drawings POWDERED POLYSACCHARIDE-REINFORCED ELAS'IOMER MASTERBATCHES, COMPOUNDS, AND RESULTING VULCANIZED RUBBERS A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

BACKGROUND OF THE INVENTION This invention relates to processes for producing powdered elastomer compositions. The invention more specifically relates to powdered elastomer compositions from which vulcanized rubber can be directly prepared. A particular aspect of the invention concerns extensions of and improvements over the inventions described by Buchanan et al., US. Pat. Nos. 3,442,832, 3,480,572, and commonly assigned copending application Ser. No. 859,195, filed Sept. 18, 1969, of Stephens et al., which disclosures are incorporated herein by reference.

The instant invention provides the first example of potentially low-cost, storage-stable, general-purpose, powdered rubber compounds suitable for a wide range of applications. It

- is well known that availability of general-purpose elastomer compounds in powdered form has the possibility of revolutionizing the rubber industry by eliminating the need for costly high shear mixing and the consequent need for heavy duty mixing equipment typified by Banbury mixers. It is desirable to have powdered elastomers such that powder processing techniques common to the plastics industry can beemployed in manufacture of rubber goods.

Finely divided elastomers have been prepared by spray drying of latex mixtures, but this method is inherently high in cost and has many other attendant difficulties as discussed by Redberg et al., US. Pat. No. 3,194,781. Also, powdered elastomers have been prepared by co-coagulation with water glass as disclosed by Maass et al., U.S. Pat. Nos. 3,190,851 and 3,257,350; but this method is also impractically expensive :besides giving products of limited application because of the high silica loading (50 parts per 100 parts elastomer, phr). Certain other methods for preparation of powdered elastomers have been suggested or attempted; for example, making a 1 percent solution of elastomer, then cooling the solution below the glass transition temperature of the elastomer before coagulation. However, all such methods involving very low temperatures and/or high dilutions are also economically prohibitive.

What has been needed is a low-cost, high-production-rate process for comminuting elastomers to fine particle size. But it is well known that direct grinding of ordinary elastomer crumb or slab is impractical because the heat generated causes it to become extremely tacky and it sticks to internal mill parts, clogging the machine as well as causing excessive power consumption. Elastomers have been ground or pelletized to coarse powders (ca. l-inch particle diameters) by admixture of undesirable and expensive detackifying agents such as polystyrene dust. Elastomers might also be ground under extreme conditions at dry ice temperatures below the polymer brittle point. However, all prior art comminuted elastomers reagglomerate or more usually adhere to form a single mass upon storage. So also do most of the powders formed by spray drying or co-coagulation methods.

In the United States, one powdered specialty elastomer has recently become available, a nitn'le at a high premium price as compared to the same slab elastomer. The price premium on this powdered nitrile attests to both the difficulty of production and the utility of powdered elastomers. Despite widespread interest, free-flowing, general-purpose, powdered elastomers remain unavailable because no practical method for their preparation existed prior to our invention.

In the patents of Buchanan et al., supra, it was disclosed that polysaccharide-elastomer coprecipitates are obtained by simultaneously crosslinking polysaccharide and destabilizing latex particles in mixtures of polysaccharide solutions and latices. 'Ihe-polysaccharide-elastomer coprecipitates are oven dried to provide hard-curd particles in which the dry polysaccharide constitutes the continuous phase and elastomer particles the discontinuous phase. In the Buchanan patents it was disclosed that extensive high shear mixing as on a differential roll mill or equivalent machine was required to produce phase inversion and give useful rubber products with a fine particle dispersion of polysaccharide in elastomer matrix. In the copending application Ser. No. 859,195, it was further disclosed that hot mechanical working in a closed machine with moisture present during the phase inversion is advantageous. This phase inversion is obviously a critical step in the process of producing polysaccharide-reinforced rubbers since such composite materials must have an elastomeric matrix in order to have high elastic properties or rubbery" character. Furthermore, reinforcement of elastomers requires the good dispersion of hard, fine particle filler achieved by breaking up the original polysaccharide matrix during the phase inversion.

A primary object of the invention is to provide powdered rubber compounds suitable for direct heat-compression or injection molding to give finished, vulcanized rubber products, thus making the powder processing techniques long employed by the plastics manufacturing industry available to rubber processors for the first time.

Another object of the invention is to provide powdered elastomer masterbatches suitable for direct blending with curatives and other ingredients to provide completely and thoroughly mixed compounds ready for molding and vulcanizing, thereby completely eliminating or greatly reducing the need to employ expensive, conventional high shear rubber mixing equipment and processes.

Another object of the invention is to provide a method for producing general-purpose elastomer powders by a low-cost, high-production-rate, direct grinding process.

In accordance with the above-stated objects, we have discovered a method for making powdered polysaccharidereinforced elastomer masterbatches. The method comprises coprecipitating polysaccharides with elastomers, drying the coprecipitates, and comminuting the coprecipitates. The polysaccharide can be any one of the following: starch xanthide, zinc starch xanthate, resorcinol-formaldehydetreated zinc starch xanthate, lignin and starch xanthide in combination, resorcinol-formaldehyde-treated gelatinized starch, and their cereal flour analogs. Elastomers can be styrene-butadiene rubber, oil-extended styrene-butadiene rubber, nitrile rubber, and phenol formaldehyde resin-extended nitrile rubber.

Storage-stable, readily curable, powdered polysaccharidereinforced rubber compounds can be made by blending powdered polysaccharide-reinforced elastomer masterbatches with normally used rubber curatives (i.e., those used in industry such as zinc oxide, sulfur, antioxidant powder, etc.). Besides the curatives, fillers and extenders such as clay, highly reinforcing silica, or carbon black can be incorporated in the rubber compounds.

We have also discovered a method for making vulcanized rubber by direct shaping, molding, and curing of powdered polysaccharide-reinforced rubber compounds with very little prior shear mixing. The shaping and molding are accomplished by the combined action of heat and compression on the powder.

DETAILED DESCRIPTION OF THE INVENTION elastomer occurs. Rubber articlescquivalent to. products obtained by practicing the inventions of. the Buchanan patents may be made by fine grinding dried polysaccharide-elastomer curd and then molding the resulting powder. Such articles are fully satisfactory for a large variety of applications. This accomplishment seems at first to be completely contradictory and opposed to all our earlier teaching that high shear mixing and mechanical working to bring about extensive flow of elastomer matrix is necessary to produce phase inversion as needed for rubbery properties. However, having 'made the unexpected discovery of the present invention, we now reason that grinding of the drypolysaccharide-rubber curd produces incipient phase inversion by breaking up the continuous polysaccharide phase to fine particle size in combination with a very limited hot-flow which may occur during impact in conventional comminuting apparatus. Then the phase inversion process must become completed as a result of the further very limited flow occurring in the heat-compression or other molding process. The above explanation may not be entirely correct, but, regardless of the mechanism involved, it is now apparent that phase inversion from rubber particles in a polysaccharide matrix to polysaccharide particles in a rubber matrix may conveniently be accomplished by a process involving comminuting dry polysaccharide-rubber coprecipitates followed by heat-compression, extrusion, or injection moldrng..

We have found that grinding of dry polysaccharideelastomer coprecipitate is facile and gives free-flowing, fine powders. The resulting powdered masterbatches are easily blended with usual powdered curatives to give storage-stable powdered rubber compounds. These powdered compounds can be directly molded into rubber articles in ordinary heated compression molds. The powders can also be formed into finished rubber articles by extrusion from a simple machine with no prior shear mixing; hence, also by injection molding. When desirable, the powdered polysaccharide-rubber compounds per se can be advantageously shaped into mold blanks or further mixed with additional ingredients on differential rolls, or with extruders before shaping into mold blanks. Thus, much less shear mixing is required than for conventional rubber processing.

For grinding polysaccharide-rubber compositions, any of the common commercial comminuting machines may be employed, i.e., impact mills such as hammer, Wiley, and pin mills, etc. Grinding may include air or screen classification with recycle of coarse fractions to the grinders as conventionally practiced in order to further reduce average particle size. We find it advantageous, but not essential, to incorporate small amounts of anticaking substances into powdered rubber masterbatches. Fine particle fumed or hydrated silicas are preferred because these materials are further useful for their reinforcing ability in the finished rubbers. Generally, we employ up to l phr of hydrated silica (PPG Hi-Sil 215) which has been pelletized and is therefore advantageously added during the grinding operation to achieve both disintegration of pellet and distribution throughout the powdered rubber masterbatch. Additional fillers and extenders such as clay, highly reinforcing silica, and carbon black can also be used.

Compounding of polysaccharide-rubber masterbatch powders may be accomplished with V or ribbon blenders if added ingredients are fine powders. If flaked, pelletized, or encapsulated compounding ingredients are added, high-speed rotary blade powder mixers, such as the Waring Blendor or Henschel mixer, are preferred.

This invention may be practiced with any of the polysaccharide-rubber compositions disclosed in the reference patents (3,442,832 and 3,480,572) and copending application (859,195). Accordingly, any elastomer available in latex form may be employed including natural rubber or preferably synthetic elastomers such as nitrile and SBR. Suitable polysaccharidesinclude starches, starch derivatives, cereal flour, and derivatives thereof. Examples of applicable starch products are gelatinized starches, arninated starches, xanthated starches, resin-treated starches, starch xanthides, and similar derivatives as well as their cereal flour analogs, etc. Polysaccharide loading must exceed about 15 phr for easy grinding. There is no upper limit on polysaccharide loading, but the cured products undergo a transition from elastic vulcanized rubbers to rigid thermoset plastics as starch loading increases above about phr. For elastic vulcanized rubbers, we prefer to use relatively low polysaccharide loadings, from 15 to 30 phr, in order to allow more freedom for addition of conventional fillers during compounding, thus increasing the area for application of the powdered elastomer masterbatches. For rigid thennoset plastic applications, we prefer to use relatively high polysaccharide loadings, from 100 to 400 phr, so that the total composition contains not more than about 70 weight percent elastomer plus resin combined.

The following examples are included as further illustrations of the invention but not as limitations thereon.

EXAMPLE 1 The starting materials included type 1502 SBR (styrene-butadiene) latex containing 20.5 percent total solids and a 10 percent aqueous starch xanthate solution with xanthate degree of substitution (D.S.) of 0.1 1.

For a starch xanthide-SBR-l502 coprecipitate containing 20 phr starch (20 parts starch per 100 parts SBR), a homogeneous mixture was prepared containing 800 g. starch xanthate solution, 1,950 g. SBR-l502 latex, 8 g. of 50 percent styrenated phenol antioxidant emulsion, and 6 g. sodium nitrite. This mixture was stirred for 30 minutes, then ml. of 2 N sulfuric acid were slowly added dropwise with stirring to give a pH of 4.0-4.5 and maintain it for 10 minutes. This treatment coprecipitated starch xanthide and SBR-l 502 elastomer as large curd particles. The curds were recovered by filtration, washed once by suspension in water, then dried in a forced draft oven at 70 C. to give 476 g. of dried starchrubber coprecipitate.

Another starch xanthide-SBR-l502 coprecipitate having 30 phr starch was prepared in the same manner with the same quantities of latex and antioxidant, but using 1,200 g. starch xanthate solution, 7.6 g. sodium nitrite, and 253 ml. of 2 N sulfuric acid. This gave 503 g. of dried starch-rubber coprecipitate.

A third starch xanthide-SBR-ISOZ coprecipitate having 45 phr starch was also prepared based on the same amount of latex. This product weighed 580 g.

Since the oven-dried curds were too large for the feed screw of our laboratory hammermill, each product was first ground to pass a 3 mesh screen on a small Wiley mill. The coarse ground coprecipitates were then ground through a 16 mesh screen by an ordinary agricultural-type hammer-mill. Each powder was then mixed with 20 g. of hydrated silica in a Waring Blendor for 30 seconds. Screen analyses of the resulting free-flowing powders gave the following values:

Each masterbatch powder was mixed with l phr flake stearic acid, 4 phr zinc oxide, 2 phr sulfur, 2 phr antioxidant powder, 1.5 phr benzothiazyl disulfide accelerator, and 0.1 phr tetramethylthiuram disulfide secondary accelerator for 30 seconds at high speed in a Waring Blendor. Each resulting rubber compound was then divided into two equal portions.

One portion of each compound was consolidated into mold blanks suitable for preparing standard ASTM test specimens by passing through a tight nip on a differential roll mill for three passes, then sheeting out to the required thickness with a minimum of further milling. This mold blank forming process required less than one-tenth of the high shear mixing time needed for conventional rubber processing, i.e., as described by ASTM method DIS-68a for example. Oscillating disc without washing, in a forced draft oven at 70 C.,'giving 487 g.

rheometer cure data were obtained using these mill-formed of product.

blanks for each compound, and all vulcanized test specimens Other zinc starch xanthate-SBR-l502 products containing were prepared using the rheometer optimum cure time at 150 30 hr and 45 hr tar h, ti l were prepared b h 5 same process using increased amounts of starch xanthate solu- The other portion of each powdered rubber compound was tion and acid but the same quantities of other reagents. There subdivided, and test specimens were prepared by direct were 536 g. and 6l 1 g. of these twoproducts, respectively.

powder molding. A thin flat rubber sheet for tensile specimens All three samples were ground by the procedure of Example was prepared by molding powder directly between flat plates. 1 except that the 20 g. of hydrated silica were added before A small rubber dish was compression molded and cured for 10 grinding through the hammermill. Their screen analyses were examination. Rods, one-quarter inch in diameter, were as follows:

prepared from powder feed by extrusion at 125 C. with a i l Particle diameters, 955111811" Brabender-Plasticorder equipped with 10/ 1 length to diameter composmm 1,410 n 840 u 590 p. 420 a 350 a ratio extrusion head and then post-curing the extrudate in an oven. 15 :3 p21 starch 100 87.5 74.3 55.7 45.7

. t h 100 6. Representative physical test data for these various specimen 45 S 2:2 100 gig types are given in the following table:

Ultimate Starch Cure Hard- Tensile elonga- Dish, loading, time, ness, strength, tion, utility, and phr. Treatment min. Shore A p.s.i. percent appearance Mill consolidation. 17 70 1, 560 475 20 Powder molding 760 220 Excellent.

Powder extrusion l, 155 {Mill consolidation l7. 5 77 1,110 330 Powder molding. 17. 5 1, 050 200 Excellent.

Mill consolidation. 15. 5 83 1,620 260 Powder molding. 15. 5 1, 070 130 Good.

Powder extrusion. 15. 6 1, 090

Remaining portions of these powdered starch xanthide- 30 These masterbatch powders were compounded withaWar- SBR-l502 compounds were stored at room temperature for ing Blendor as in Example 1 except that addition of zinc oxide 10 weeks. At the end of this storage period, they remained was not required. Vulcanized test specimens were prepared as free-flowing, and their rheometer cure curves remained in Example 1 and their test values are given below:

Starch Cure Tensile Ultimate loading, time, Hardness, strength, elongation, Dish, utility, and phr. Treatment I min. Shore A p.s.i. percent appearance 20 {Mill consolidation 21 63 1, 860 720 Powder molding. 21 1,150 570 Excellent, translucent.

Powder extrusion 21 1,163 30 Mill consolidation 17. 5 72 1,600 510 Powder molding 17. 5 1,110 380 Excellent, translucent. Powder extrusion 17. 5 1, 800 45 Mill consolidation 12 83 1, 320 450 Powder molding 12 710 40 Satisfactory.

Powderoxtrusion" 12 840 unchanged, i.e., completely identical with the initial curves The above data clearly show that zinc starch xanthate-SBR made soon after compounding. Thus, these powders were powdered rubber compounds are fully equal or superior to the completely stable to indefinitely long storage. starch xanthide containing powders. We believe that the com- Although the above physical test data appear to indicate pound containing only 20 phr zinc starch xanthate is espethat mill consolidation of the powdered compounds results in i ll eful because of the strong, very elastic, light-colored,

better vulcanizate strength than the other treatments, the translucent rubber articles which can be directly molded from ference in test values is due in part to inaccuracies associated hi d Because i h a l starch l di this with testing the nonstandard specimens prepared y th dered compound is very amenable to extension with addipowder-forming processes. The inaccuracies arise because rimfille a d extenders as well as with additional high-reinsuch specimens are hard I lamp prope y in Our test forcing agents. Thus, it is a very versatile product with a wide machine. We believe that the properties of the extruded range ofappfications shapes are actually fully equivalent to those of the mill consolidated specimens. The data clearly show that rubber articles with technically useful and acceptable properties can be EXAMPLE 3 prepared by direct molding of this invention's powdered compounds and that these compounds are suitable for direct feeding to Screw injection molding machines- Four powdered masterbatches were prepared from starting xanthate solutions containing 10 percent of corn flour, soft EXAMPLEZ wheat flour, hard wheat flour, or unmodified corn starch,

Latex and starch xanthate starting materials were the same respectively. These masterbatches contained 30 phr as in Example l. amylaceous material and were made by coprecipitation with For a zinc starch xanthate-SBR-l502 coprecipitate containzinc according to the procedure of Example 2. However, 3.27 ing 20 phr starch, a homogeneous mixture was prepared cong. of resorcinol and 7.2 g. of 37 percent formalin were added taining 800 g. starch xanthate solution, 1,950 g. SBR-l502 to each xanthate-latex mixture during the 30-minute agitation latex, and 8 g. of 50 percent styrenated phenol antioxidant period preceding the coprecipitation. Samplesize wasbased emulsion. This mixture was agitated for 30 minutes; then 24 on 1,950 g. of 83114502 lat r d d product i h were ml. of 2 N sulfuric acid were added dropwise, followed by 537 g., 541 g., 532 g., and 536 g. for cornflour, soft wheat rapid addition of 198 ml. of M zinc sulfate solution. The flour, hard wheat flour, and starch products, respectively. resulting coprecipitate was recovered by filtration and dried, Screen analyses were asfollows:

Masterbatch Particle diameters, smaller than Starch 100 84.5 58.2 34.0 24.3 composition 1,410 p. 840 p. 590 p. 420 p. 350 y.

Corn flour 100 97.8 85.6 59.9 46.6 Soft wheat flour X 96.4 84.2 63 50.9 Hard whent flour 100 972 86.9 661 53.9 They were compoundedby vinth powdered curatives starch 100 79,5 51.2 m the Waring Blendor, optimum curing conditions were determined, and vulcanized test specimens were prepared.

Cure Hard- Abrasion 'lensilc Ultimate time, ness, resistance, strength, elongation. Product Treatment min. Shore A percent p.s.i. percent Mill consolidation. 30. 5 51) 100 1,380 7 10 Gem flour. Power molding 30. 5 1, 140 430 Powder extrusion 30. 5 1, 010 Mill consolidation. 35 67 120 1,530 500 Starch "{Powder molding.. 35 1,420 370 Powder extrusion 35 1,167

These powdered masterbatches were compounded without added zinc oxide and vulcanized test specimens were prepared as in Example 2. Representative physical test data are given below:

This example illustrates use of resin crosslinked gelatinized starch as an alternative to starch xanthate derivatives in practice of the invention. Resulting vulcanizates have somewhat different properties than are obtained with xanthate deriva- Curo Abrasion Tensile Ultimate time, Hardness, resistance, strength, elongation,

Product Treatment min. Shore A percent p.s.i. p.s.i.

Mill consolidation 74 109 2, 180 480 Corn flour Powder molding 30 1, 450 320 Powder extrusion. 30 800 Mill consolidation 30 76 133 2, 040 415 Soft wheat flour Powder molding 1, 600 310 Powder extrusion 2,085

Mill consolidation 1, 830 350 Hard wheat flour Powder molding l, 580 350 Powder extrusion 2, 025

Mill consolidation Z, 200 400 Starch Powder molding 1, 510 270 Powder extrusion ,80O

The above surprisingly good abrasion resistance values were tives. But as in Example 3, each powdered compound gave obtained with the DuPont abrader and are relative values. Vulcanizates made from commercial type 1606, 52 phr HAF black reinforced, SBR masterbatch were assigned abrasion resistance value of 100 percent.

Each of the above powdered compounds gave an excellent highly elastic, brown, translucent dish with a polished surface by direct molding from powder. I

This example illustrates that a variety of low-cost amylaceous materials can be employed in place of refined starches in practice of the invention. It also shows the marked improvements obtained by treatment of the incorporated polysaccharides with resorcinol-formaldehyde.

EXAMPLE 4 a hot com flour paste containing 19.96 percent solids was prepared by steam-jet cooking at 340 F. with a Penick and Ford laboratory cooker described in their US. Pat. No. 3,133,836. Similarly, a hot unmodified corn starch paste was prepared containing 19.71 percent solids.

Homogeneous mixtureswere made immediately from 545 g. of the hot corn flour paste and 5 72 g. of the hot starch paste, respectively, with added 8 g. of 50 percent sodium hydroxide, 1,950 g. of SBR-i502 latex, 8 g. of 50 percent styrenated phenol antioxidant emulsion, 4.9 g. of resorcinol, and 4.0 g. of paraformaldehydc. Each of these mixtures was stirred 30 minutes then coprecipitated by addition of 185 ml. M zinc sulfate solution. The soft curd products were recovered by filtration and dried in a forced draft oven at 70 C. Dry weights were 527 g. and 519 g. for corn flour resin and starch resin products, respectively. They contained 30 phr of resin-treated amylaceous material wherein 0.06 mole of resorcinol per 162 g. of cereal raw material was incorporated.

These products were ground by the procedure of Example 2 with results as follows:

vulcanizates with surprisingly good abrasion resistance. They also gave excellent quality dishes by direct molding from powder.

EXAMPLE 5 Starch Lignin Product Sample No. loading, loading, weight,

phr phr g.

78 l5 1 3 535 80 I5 26 595 12 30 l 3 596 81 3O 26 699 Sample No. 12 was ground by the procedure of Example l. No hydrated silica was subsequently added even though lignin is somewhat deleterious in its effect on caking of these powders. Sample No. 78 had 5 phr hydrated silica incorporated during grinding as in Example 2. Samples No. 80 and 81 were ground once through the hammermill with added 3 phr hydrated silica then screened on a 30 mesh screen. Then the coarse fraction from samples 80 and 81 was reground through the hammermill with an additional added 2 phr hydrated silica and recombined with its fine fraction. Screen analysis of these powdered masterbatches follow:

Particle diameters, smaller than Sample No. 91 contained 400 phr of resorcinol-formaled- Sample r410 P 840 590 I 420 I 350 P hye-treated zinc corn flour xanthate and 400 phr phenol-formaldehyde resin. It was made as above using 3,000 g. 78 100 94.7 82.0 56.2 40.7 xanthate, 190 g. NBR latex, 449 g. resole syrup, 2 g. antioxi- 80 100 98 dant emulsion, 8.3 g. resorcinol, 19.5 g. 37-percent formalin, 12 35 26512N lf' 'd d198 1M lftThd 81 100 989 954 TM 583 m. su uric acl an m. zrnosu a e. e ry product weighed 584 g. 1

Each of these products was ground as in Example 1. Three 10 phr of hydrated silica were added to sample No. 87 during Vulcanizates made by compounding and curing the above compounding but not to the others. All gave perfectly freepowdered masterbatches had the following properties: flowing powders as follows:

Cure Hard- Tear Tensile Ultimate Sample time, ness, strength, strength, elongation, number Treatment min. ShoreA lb./in. p.s.i. percent Millconsolidated 2,340 815 78 1,720 700 1,595 2,600 660 80 Powder mo1ded 1,980 600 Powder extrusioln. 1,505 I Mill consolidated 1,880 365 12 {Powder molded 1,040 200 Powder extrusion. 1,155

Mill consolidated 2, 100 500 -81 Powder molded .1 980 290 Powder extrusion. 1, J

This example illustrates that the invention can be practiced Particle diameters, srrraller than advantageously with the previously disclosed synergistic Sample L410 840 590 420 350 starch-lignin reinforcing agents. Each of the above powdered 30 rubber compounds gave hlgh-quahty rubber articles by direct 7 100 985 92.3 786 691 molding 88 100 98.6 93.1 82.2 75.6

90 100 98.3 97.2 89.9 82.6 EXAMPLE 6 91 100 99.3 98.1 90.0 82.9

Starting materials for the preparations describedherein include an aqueous 10 percent corn flour xanthate solution with S l 7 and 3 were powder blended i rubber xanthate D.S. 0.04, water-dispersible phenol-formaldehyde fives, cured, and tested as in pwvious examples Their 1- resole syrup containing 66.8 percent solids, and Chemigum canizate properties are tabulated below:

Cure Tensile Ultimate Dish. Sample time, Hardness, strength, elongation, utility, and number Treatment min. Shore A p.s.i. percent appearance Mill cons0lidated 24.5 78 1,640 360 87 Powder molded 24.5 1,400 250 Excellent. Powder extrusion 1,190 Mill consolidated" 2,080 340 88 Powder mo1ded 1,160 130 Excellent. Powder extrusion. 1, 210

236 NBR (nitrile) latex containing 39.9 percent solids.

Sample No. 87 contained 20 phr of resorcinol-formaldehyde-treated zinc corn flour xanthate and no phenol-formaldehyde resin. A homogeneous mixture was prepared from 800 g. of xanthate solution, 1,002 g. of NBR latex, 8 g. of 50 percent antioxidant emulsion, 2.2 g. of resorcinol, and 4.8 g. of 37 percent formalin. The mixture was agitated for 30 minutes, then 15 ml. of 2 N sulfuric acid were added dropwise followed by rapid addition of 198 ml. of M zinc sulfate solution. The coprecipitated curd was recovered by filtration and dried in a forced draft oven at 70 C. giving 507 g. of product.

Sample No. 88 contained 25 phr of resorcinol-formaldehyde-treated zinc corn flour xanthate plus 25 phr of phenolformaldehyde resin. It was prepared in the same manner as above using the same quantities of latex, antioxidant, and zinc but using b 1,000 g. of xanthate, 148 g. of resole syrup, 2.7 g. of resorcinol, 6.1 g. of formalin, and 50 ml. of 2 N acid. The dry product weighed 626 g.

Sample No. 90 contained 100 phr of resorcinol-formaldehyde-treated zinc corn flour xanthate and 100 phr of phenol-formaldehyde resin. It was coprecipitated by the above method using 2,000 g. xanthate, 501 g. NBR latex, 296 g. resole syrup, 5.5 g. resorcinol, 13 g. formalin, 4 g. antioxidant emulsion, 115 ml. 2 N sulfuric acid, and 198 ml. M zinc sulfate. The dry product weighed 561 g.

Samples and 91 were treated as phenolic resin molding compounds. Sample 90 was blended in a Waring Blendor with 2.0 g. stearic acid, 27.7 g. calcium oxide, 4.0 g. sulfur, 3.0 g. antioxidant, 3.0 g. benzothiazyl disulfide, and 0.2 g. tetramethylthiuram disulfide. Sample 9i was blended with 0.7 g. stearic acid, 26.4 g. calcium oxide, 1.4 g. sulfur, 1.0 g. antioxidant, 1.0 g. benzothiazyl disulfide, and 0.1 g. tetramethylthiuram disul fide. Both these powder compounds were densified by passing through the nip of a steam-heated differential roll mill for five passes. The densified material was removed from the roll with a doctor knife after each pass. The densified powders were then cured 20 minutes at 150 C. in various compression molds. Molded articles were produced including dishes of the type examined in previous examples. These articles were thermoset plastics with hard smooth finish, excellent appearance, good water resistance, and highimpact resistance. Articles made from sample 90 were slightly flexible.

EXAMPLE 7 A free-flowing powdered zinc starch xanthate-oil-extended elastomer masterbatch was prepared by the method of Example 2. It contained 20 parts starch and 10 parts silica per parts oil plus elastomer; the oil to'elastomerratio was 1 /2. .The

but with additional tillers except samples 92-1 and 92-6 which had no additional fillers. Sample 92-2 had an additional 30 phr of hydrated silica, .92-3 had 5 2 phr hard clay, 92-4 had 18 phr ASTM reference black No. 2 (HAP), 92-5 had 36 phr of the No. 2 reference black, and 92-6 was the 66-g. portion of masterbatch compounded exactly as 92-1 for comparative powder, molding. "l'he first five of these compounds were mill consolidated into mold blanks, cured, and test specimens prepared. Vulcanizate properties follow.

Hum ilu Hpuollln Imus, strength, lus, strength, lion num mr gravity Show A ll ./lu. p.s.i. p.s.i. pare-an it is evident from the foregoing data that this invention provides even highly oil-extended, general-purpose, elastomer powders entirely suitable for compounding with high loadings of a variety of additional reinforcing agents, fillers, and extenders.

We claim:

1. Powdered starch xanthide-styrene-butadiene rubber elastomer masterbatches containing from 20 to 45 phr starch, having nearly all particles below 1,410 1. diameter and more than 50 weight percent below 420 p. diameter, and which provide vulcanized rubbers having greater than about 760 p.s.i. tensile strength, greater than about 70 Shore A hardness, and greater than about 130 percent ultimate elongation.

2. Powdered zinc-starch xanthate-SBR elastomer masterbatches containing from 20 to 45 phr starch, having nearly all particles below 1,410 1. diameter and more than 45 weight percent below 350' p. diameter, and which provide vulcanized rubbers having greater than about 710 p.s.i. tensile strength, greater than about 63 Shore A hardness, and greater than about 40 percent ultimate elongation.

' 3. Powdered lignin-starch xanthide-SBR elastomer masterbatches containing from to 30 phr starch and from 13 to 26 phr lignin,.having nearly all particles below 1,410 p, diameter and more than 63 weight percent below 840 p, diameter, and which provide vulcanized rubbers having greater than about 980 p.s.i. tensile strength, greater than about 67 Shore A hardness, and greater than about 200 percent ultimate elongation.

4. Powdered zinc starch xanthate-oil-extended SBR elastomer masterbatch containing about 20 phr starch based on total 'oil .plus SBR polymer, having nearly, all particles below 1,410 a diameter and more than 54 weight percent below 350 p. diameter, and which provides vulcanized rubbers having greater than about 600 p.s.i. tensile strength, greater than about 49 Shore A hardness, and greater than about 250 percent ultimate elongation.

5. A method for making free-flowing powdered polysaccharide-reinforced elastomer masterbatches capable of forming vulcanized rubber products by heat-compression or injection molding with little or no prior phase reversion which comprises: I a. coprecipitating a'polysaccharide selected from the group consisting of starch xanthide, zinc starch xanthate, lignin and starch xanthate in combination, and their cereal flour analogs with an elastomer'selected from the group con sisting'of styrene-butadiene rubber, oil-extended styrenebutadiene rubber and nitrile rubber; b. drying the resulting coprecipitates; I c. grinding the'dried coprecipitates to a free-flowing powder in which substantially all particles have diameters of less than 1,410 and d. optionally blending the powdered coprecipitates with normally used rubber curatives, fillers, extenders, or reinforcing agents. v

6. Reinforced vulcanized rubber prepared from powdered starch xanthide-SBR elastomer masterbatches described in claim 1 blended with normally used rubber curatives, said rubber being characterized as having greater than about 760 p.s.i. tensile strength, greater than about 70 Shore A hardness, and greater than about percent ultimate elongation.

7. Reinforced vulcanized rubber prepared from powdered zinc starch xanthate-SBR elastomer masterbatches described in claim 2 blended with normally used rubber curatives, said rubber being characterized as having greater than about 710 p.s.i. tensile strength, greater than about 63 Shore A hardness, and greater than about 40 percent ultimate elongation.

8. Reinforced vulcanized rubber prepared from powdered lignin-starch xanthide-SBR elastomer masterbatches described in claim 3 blended with normally used rubber curatives, said rubber being characterized as having greater than about 980 p.s.i. tensile strength, greater than about 67' Shore A hardness, and greater than about 200 percent ultimate elongation.

9. Reinforced vulcanized rubber prepared from powdered zinc-starch xanthate-oil-extended-SBR elastomer masterbatches described in claim 4 blended with normally used rubber curatives, said rubber being characterized as having greater than about 600 p.s.i. tensile strength, greater than about 00048and greater than about 250 percent ultimate elongation. 

2. Powdered zinc starch xanthate-SBR elastomer masterbatches containing from 20 to 45 phr starch, having nearly all particles below 1,410 Mu diameter and more than 45 weight percent below 350 Mu diameter, and which provide vulcanized rubbers having greater than about 710 p.s.i. tensile strength, greater than about 63 Shore A hardness, and greater than about 40 percent ultimate elongation.
 3. Powdered lignin-starch xanthide-SBR elastomer masterbatches containing from 15 to 30 phr starch and from 13 to 26 phr lignin, having nearly all particles below 1,410 Mu diameter and more than 63 weight percent below 840 Mu diameter, and which provide vulcanized rubbers having greater than about 980 p.s.i. tensile strength, greater than about 67 Shore A hardness, and greater than about 200 percent ultimate elongation.
 4. Powdered zinc starch xanthate-oil-extended SBR elastomer masterbatch containing about 20 phr starch based on total oil plus SBR polymer, having nearly all particles below 1,410 Mu diameter and more than 54 weight percent below 350 Mu diameter, and which provides vulcanized rubbers having greater than about 600 p.s.i. tensile strength, greater than about 49 Shore A hardness, and greater than about 250 percent ultimate elongation.
 5. A method for making free-flowing powdered polysaccharide-reinforced elastomer masterbatches capable of forming vulcanized rubber products by heat-compression or injection molding with little or no prior phase reversion which comprises: a. coprecipitating a polysaccharide selected from the group consisting of starch xanthide, zinc starch xanthate, lignin and starch xanthate in combination, and their cereal flour analogs with an elastomer selected from the group consisting of styrene-butadiene rubber, oil-extended styrene-butadiene rubber and nitrile rubber; b. drying the resulting coprecipitates; c. grinding the dried coprecipitates to a free-flowing powder in which substantially all particles have diameters of less than 1,410 Mu ; and d. optionally blending the powdered coprecipitates with normally used rubber curatives, fillers, extenders, or reinforcing agents.
 6. Reinforced vulcanized rubber prepared from powdered starch xanthide-SBR elastomer masterbatches described in claim 1 blended with normally used rubber curatives, said rubber being characterized as having greater than about 760 p.s.i. tensile strength, greater than about 70 Shore A hardness, and greater than about 130 percent ultimate elongation.
 7. Reinforced vulcanized rubber prepared from powdered zinc starch xanthate-SBR elastomer masterbatches described in claim 2 blended with normally used rubber curatives, said rubber being characterized as having greater than about 710 p.s.i. tensile strength, greater than about 63 Shore A hardness, and greater than about 40 percent ultimate elongation.
 8. Reinforced vulcanized rubber prepared from powdered lignin-starch xanthide-SBR elastomer masterbatches described in claim 3 blended with normally used rubber curatives, said rubber being characterized as having greater than about 980 p.s.i. tensile strength, greater than about 67 Shore A hardness, and greater than about 200 percent ultimate elongation.
 9. Reinforced vulcanized rubber prepared from powdered zinc-starch xanthate-oil-extended-SBR elastomer masterbatches described in claim 4 blended with normally used rubber curatives, said rubber being characterized as having greater than about 600 p.s.i. tensile strength, greater than about 49 Shore A hardness, and greater than about 250 percent ultimate elongation. 